The present invention relates to nonferrous metallurgy, and more particularly to methods of complex processing molten slags in electric furnaces with a purpose of recovering heavy metals (such as zinc, lead, copper, nickel, cobalt) and iron therefrom.
There are known in the art methods of processing molten slags produced, for example, by nickel smelting or containing low-grade tin concentrates, by their filtration through heated coke or coal filters. The prior-art methods envisage reducing metal oxides from the slags passed through a coke filter at a temperature of 1700.degree. C. and over. The degree of reducing the metal oxides is adjusted by varying the height of a coke bed, its temperature and the time period during which the slag passes through the coke filter. This results in complete recovery of the nickel and cobalt, and that of 65% of iron from the slag.
The disadvantages of said prior-art methods reside in high power inputs for heating a coke filter and maintaining its temperature at 1700.degree. C. and over, complicated servicing and the need for additional equipment.
There is likewise known in the art a method of treating slags produced in nickel smelting in an electrically-heated hearth with a coke filter. The hearth is formed of two vessels differing in height and communicating in their bottom part through a channel partly filled with a layer of molten matte. The slag is poured into the top area of said hearth wherein it is subjected to filtration at first through a layer of coke and then through a matter layer, flowing thereafter along the channel into the bottom area of the hearth to be settled out therein.
However, a single transitory filtration of said slag passing in a layer of non-uniform thickness through the coke filter fails to provide a requisite degree of reduction of metal oxides with the resultant low rate of removing said metal oxides from the slag.
There is also known in the art a method of recovering tin from low-grade concentrates by reduction smelting in an electric furnace in the presence of silica and sulphureous materials. Smelting of an initial charge is effected on a coal filter at temperatures sufficient to enable partial reduction of silica.
The aforesaid method also suffers from the disadvantage that it requires high power inputs for heating a carbonaceous filter and maintaining its temperature above 1500.degree. C.
Moreover, the servicing of said electric furnace is coupled with difficulties stemming, firstly, from a need to maintain the requisite temperature of said coke filter, which presents a problem in view of the variable electrical conductivity of a layer, responsive to the degree of reducing oxides; secondly, from the difficulty to sustain a constant rate of filtration which tends to change as the coke particles burn out; thirdly, from the accumulation and tapping of both the slag and a high-melting-temperature ferriferrous alloy, and finally from a need for additional equipment.
Known likewise in the art is a furnace divided by a partition into two parts and adapted for flash smelting of finegrained materials. In one part said materials are flash-smelted, the slag flowing through a port in the bottom part of said partition into the second part of the furnace, wherein are mounted electrodes which provide for both the heating of said slag and its stirring due to natural convective motion (see, e.g., Inventor's Certificate of the USSR No. 190578).
However, the aforedescribed furnace is not provided with any means for adjusting the stirring rate, which results in a low rate of reducing metal oxides from the slags, as well as in an inadequate degree of the slag depletion in terms of its valuable constituents.
There is likewise known in the art an electric furnace for smelting concentrates containing nonferrous metals, said furnace being equipped with burners mounted on its roof at an end face wall against a flue, and with a metal notch located on the opposite side. The furnace has a step-shaped hearth inclined towards said metal notch.
However, the aforesaid furnace also suffers from inadequately intensive stirring of the melt with the reducing flame of the burner mounted only on one side of the furnace which results in the low rate and degree of slag depletion.